Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures.

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8 degrees C) and warmer (12 degrees C) than normally experienced by these fish (9.5 degrees C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12 degrees C than at both 5 and 8 degrees C. Fish with different genotypes at Pgm2 and Ck1 showed significant differences in hatching time that were consistent between experiments. Ck1 heterozygotes hatched sooner than homozygotes at 8 degrees C but later at 12 degrees C. Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.